def _check_client_key(hf, stored_key, auth_msg, proof):
client_signature = hmac(hf, stored_key, auth_msg)
client_key = xor(client_signature, b64dec(proof))
key = h(hf, client_key)
if key != stored_key:
raise ScramException("The client keys don't match.")
def _c_key_stored_key_s_key(hf, salted_password):
client_key = hmac(hf, salted_password, b"Client Key")
stored_key = h(hf, client_key)
server_key = hmac(hf, salted_password, b"Server Key")
return client_key, stored_key, server_key